In my above-referenced copending patent application I disclose a harvester provided with sensor means ahead of the chassis in the transport direction for detecting the edge of a swath cut in a standing crop and for generating an output corresponding to the position of this edge relative to the chassis. Actuation means independent of the steering element and connected to the sensor means receives this output and controls the guide wheels of the chassis in accordance with this output. Further means is provided which is responsive to inclination of the ground under the chassis for altering the output so as to bias the chassis directionally in the uphill direction. Also in accordance with that invention means is provided responsive to the displacement speed of the chassis in the transport direction for altering this output so as to reduce the steering response with increasing speed and vice versa.
My earlier application further discloses feedback means responsive to the position of the steering wheels relative to the transport direction of the chassis for altering the output so as to eliminate this output when the guide wheels have made a response adequate to compensate for the alignment of the chassis with the swath, even though this compensation has not yet moved the chassis fully into the proper position along the edge of the swath.
This arrangement has shown itself to be extremely useful for crops such as wheat, oats, and the like, but is relatively ineffective when a stalk-type row crop, such as corn, is being harvested.
It is known to harvest such a stalk-type row crop using a feeler arm mounted at the front end of the chassis. This arm is pivotal about a vertical axis and normally extends perpendicular to the transport direction of the chassis so that as the chassis moves in a forward direction the arm is deflected backward by the row crop to an extent generally proportional to the position of the row transverse to the direction of displacement of the chassis. A pickoff device is connected to this arm and generates an output corresponding to the angular position of the arm, this output being used by the automatic controller operating the steering mechanism of the chassis.
Such a system has the disadvantage that even when the stalks are perfectly equispaced in the row the arm will oscillate back and forth through a predetermined angle as the chassis is displaced along the ground, the arm sliding off one stalk and then swinging forward against the next stalk under the effect of the spring urging it into a normal position perpendicular to the transport direction. Thus it is conventional in such systems to make the automatic controller relatively insensitive to this oscillation, providing it with an integrator that produces an output only when the average signal changes over a relatively long period of time. The obvious disadvantage of such a system is that the steering response is relatively sluggish.
When a gap in the row being felt by the sensor arm appears the system produces an output which is wholly false. Thus it is not uncommon when a large gap appears in the row for the harvester to veer so much off its course that it can ride over and destroy part of an adjoining row, and will necessitate manual takeover of the steering operation in order to get back on course.
An attempt to cure this false reading has been to provide a pair of sensor arms which detect the row being harvested and two locations spaced apart in the direction of travel of the machine. Both of these arms are pivoted on axes lying to one side of the row so that should one of the arms detect a gap in the row the other arm will continue to ride on the stalk. The two signals from the two arms are averaged together so as to reduce the likelihood of a false steering reaction to a simple gap in the row.
Such systems at their best are relatively insensitive so as not to be able to precisely guide the chassis along a row of stalk-type crop. Thus the operator of such harvesters must usually be on the lookout and ready to take over the steering of the machine whenever he notices that a gap in the crop appears or the machine is slowly going off course by itself.